Method:
1. Roll out the puff pastry to about Â¼ of an inch in thickness and cut it into 4 even-sized circles.
2. Spread the mustard evenly over each tart base.
3. Thinly slice the tomatoes and mozzarella and then layer over the pastry circles, leaving an edge of pastry around the outside.
4. Season with salt and pepper, sprinkle with thyme leaves and drizzle with olive oil.
5. Bake the tomato tarts for 15-20 minutes at 230.C / 440.F until the pastry is cooked through.
6. Transfer the baked tomato tarts to a warm serving plate.
7. Drizzle with the pesto and serve.